A device of this type is known from No. DE-OS 24 50 371. In the case of this known control device, the neutral electrode is divided into two segments which are separated from one another. During the time intervals in which no high frequency current flows back to the high frequency surgical apparatus via the neutral electrode, the sum of the instantaneous resistances between the two electrode-segments and the body surface is measured; the high frequency current is shut-off when this sum exceeds, or falls below, a given range.
As, in the case of this known control device, the instantaneous resistances can be measured only in the time intervals in which no high frequency current flows, changes of the instantaneous resistances in the critical phases, that is, during the flow of the high frequency current, cannot be detected. Consequently, the danger of accidental burning is present in the case of this known control device.